Defeasible deductions?

I’ve written an article that discusses the use of argumentation schemes in law, with a focus on the argumentation scheme for legal analogy. A common problem for 1L students in my experience, though, is that they apply “rule-based reasoning”—based on the deductive syllogism—a little too confidently in the beginning of their training. So for the article, I recast the deductive syllogism as a defeasible argumentation scheme.[1] I offered that argumentation scheme tentatively, as it is not the focus of the article. But now, I’d like to firm it up a little (perhaps before this article is published, but certainly before my next on related topics). What I’m interested in is whether the critical questions I offered for this argumentation scheme are the right ones.

“Anyone who operates a vehicle in a municipal park is guilty of a gross misdemeanor.”[2] Let’s assume that rule is Section 15.15 of the statutes in the State of Springer. New students confronted with this statute and the fact that a defendant rode her bicycle in the park might quickly conclude that the bicycle either is or is not a vehicle and dispose of the analysis quickly. So they might construct a perfectly valid syllogism as in Figure 1.

Figure 1: Argument by Legal Deduction in State v. Cyclist

Major Premise:                 According to Springer statutes section 15.15, any person who operates a vehicle in the municipal park is guilty of a gross misdemeanor.

Minor Premise:                 Ms. Cyclist operated a vehicle—a bicycle—in a municipal park.

Conclusion:                        Ms. Cyclist is guilty of a gross misdemeanor.

This can be generalized to the form of the deductive syllogism as in Figure 2.

Figure 2: Argumentation Scheme for Argument by Legal Deduction

Major Premise:                 According to legal authority J, in every instance with features f1 . . . fn, legal category A applies.

Minor Premise:                 The Instant Case has features f1 . . . fn.

Conclusion:                        Legal category A applies in the Instant Case.

The fact that I’ve characterized the form in Figure 2 as an “argumentation scheme” means that I’m considering it defeasible. The proponent of the argument in Figure 1 has offered a presumptively acceptable argument, but the opponent of that argument may be able to defeat it depending on the answers to several critical questions. This is where I’m interested in feedback. The critical questions I suggested in the current draft of the article are in Figure 3.

Figure 3: Critical Questions for Argument by Legal Deduction

CQ1 Acceptable Scheme Question: Is the legal rule advanced a deductive one?

CQ2 Jurisdiction Question: Does legal authority J have authority over the persons or things in the Instant Case?

CQ3 Authority Question: Does legal authority J govern the law applicable in the Instant Case?

CQ4 Rule Question: Does legal authority J actually say that legal category A applies in every instance with features f1 . . . fn?

CQ5 Exception Precedent Question: Has any legal authority identified an exception to the rule or is there any previous similar case where the rule was not applied?

CQ6 Exception Policy Question: Does the policy underlying the rule suggest there should be any exceptions?

CQ7 Instant Features Question: Does Instant Case have features f1 . . . fn?

CQ8 Feature Question: With regard to each feature f1 . . . fn, has any legal authority defined it or narrowed or expanded its definition?

Quoting from the article here (footnotes/citations omitted here):

Each of the critical questions can spawn an argument of its own regarding its outcome, the result of which may be to weaken or defeat the presumptive argument. Each question addresses one or more of the factors for assessing arguments, whether the premises and argument form are relevant, acceptable, and sufficient to support the conclusion. So, for example, with regard to CQ1, what counts as an acceptable argumentation scheme is context dependent. For example, if section 15.15 had been a factor test or other kind of legal standard, the deductive argumentation scheme would be inappropriate here.

The rest of the critical questions test the truth of the premises, CQ2–CQ6 testing the major premise and CQ7 and CQ8 testing the minor premise. CQ2 and CQ3 address the applicability of the legal authority to the current case. In our example, perhaps the alleged offense took place in one jurisdiction but J is the law in a different jurisdiction. Or perhaps J is a statute that by its own terms governs only the use of motor vehicles subject to registration with the state, but the Instant Case involves a motorized skateboard. CQ4 asks simply whether the argument’s proponent has misstated the rule. CQ5 and CQ6 consider whether there is or should be any exception to this rule. In our example under CQ5, perhaps a court concluded that a person who drives onto parkland by necessity is excused. The second prong of this question identifies where there might be an implied exception based on a previous case where the rule was not applied. As for CQ6, perhaps a legislative pronouncement identifies a policy, and giving the rule too great or too small a scope would frustrate that policy or interfere with other policy objectives of equal importance.

CQ7 asks only whether the proponent of the argument has actually asserted that all of features f1 . . . fn are present. CQ8 does the more complicated work of exploring the features to see if they are properly applied here. For example, [an earlier case may] have narrowed the definition of ‘vehicle’ in Springer statutes section 15.15. Perhaps ‘vehicle’ is defined somewhere else in Springer’s statutes that by its own terms applies to section 15.15 or that may be applied by analogy.

From the perspective of argumentation schemes, the questions that can defeat the argument—the critical questions—are those that are conventionally accepted in the field (in this case, legal argumentation) where the argumentation takes place. So, my question is: Is this the correct list of critical questions for the legal deduction argumentation scheme? I welcome your thoughts.


Photo “smart electric drive” Copyright 2012 Griin Blog, used under CC BY-NC 2.0 license (Details at

[1] My go-to as a compendium of argumentation schemes is Douglas Walton, Chris Reed & Fabrizio Macagno, Argumentation Schemes (2008). Walton, Reed, and Macagno don’t have a defeasible argumentation scheme for deduction, with the closest perhaps being “argument from rule.” Id. at 343.

[2] Adapted from H.L.A. Hart, The Concept of Law 126–27 (2d ed. 1997). See also Kent Greenawalt, Law & Objectivity 42–44 (1992) (using an ordinance requiring dogs in the park to be leashed).

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